1. Field of the Invention
The present invention relates to an OFF-state supervisory method and device of an optical repeater in which an input optical signal is converted into an electrical signal and at a state of electrical signal, after signal regeneration processing is carried out, the electrical signal is again restored to an optical signal to be output, and particularly, to an OFF-state supervisory method and device of an optical repeater which, based on a monitored value when converted into an electrical signal, a level of input optical signals can be monitored.
2. Description of the Related Art
In general, an optical signal is attenuated or degraded in an optical transmission line. An optical repeater is utilized to restore the above attenuated/degraded original signal to a pseudo-original waveform to transmit it back to the optical transmission line.
When an optical input is in an OFF state, originating from a noise output of an avalanche photodiode, a monitored value M1 is larger than the minimum value M.sub.min of monitored values when the input optical signal is not in an OFF state.
Once such ambiguous phenomenon occurs, it will not be able to discriminate whether the relevant monitored value M1 is the monitored value when an optical input is not in an OFF state or the one when the optical input is in an OFF state. Therefore, for example, when a line fault occurs, it is not discernible whether the line fault originated from an optical fiber device or from an optical repeater.